A variable valve mechanism for changing the operating angle, lift amount, and valve opening phase of a valve body that is provided in an internal combustion engine to open/close in synchronism with camshaft rotation is disclosed, for instance, by Japanese Patent Laid-open No. 2002-371816. This variable valve mechanism includes a swing arm, which is positioned between a cam and the valve body to swing in synchronism with cam operation. The swing arm is installed in the internal combustion engine with a certain degree of freedom so that the basic relative angle in relation to the valve body can be varied. This mechanism also includes a variable mechanism for varying the relative angle between the swing arm and the valve body in accordance with control shaft rotation.
When a control shaft turns within the variable valve mechanism described above, the reference relative angle between the swing angle and the valve body varies. When the relative angle varies, a change occurs in the time interval (crank angle) between the instant at which the pushing pressure of a cam begins to be transmitted to the swing arm, that is, the swing arm begins to swing due to cam action, and the instant at which the swing arm actually begins to depress the valve body. Therefore, when the control shaft rotation position is controlled, the conventional mechanism described above can vary the crank angle width (hereinafter referred to as the “operating angle”) for placing the valve body in a non-closed state as well as the lift amount to be applied to the valve body.
Further, the conventional variable valve mechanism described above is configured so that the timing for causing a cam nose to start pushing the swing arm advances when the control shaft turns in the direction of small operating angle/small lift. When such a configuration is employed, the valve opening phase of the valve body advances with a decrease in the operating angle of the valve body. It is therefore possible to ensure that the valve body opening timing remains virtually unchanged without regard to operating angle changes. The phenomenon in which the valve opening phase advances with a decrease in the operating angle as described above is hereinafter referred to as “phase coupling.”
When the conventional variable valve mechanism described above is used as an intake valve drive mechanism, it is possible to implement the so-called non-throttle type internal combustion engine. In this instance, the functionality of the variable valve mechanism can be exercised to vary the intake valve operating angle and lift amount as desired. When the intake valve operating angle and lift amount can be freely controlled, it is possible, without using a throttle valve, to exercise intake air amount control in accordance with the operating angle and lift amount. In such an instance, no intake pipe negative pressure is generated. Therefore, it is possible to reduce the internal combustion engine pumping loss.
In a non-throttle type internal combustion engine, the amount of intake air changes to a greater extent when the intake valve closing timing is changed than when the intake valve opening timing is changed. It is therefore preferred that the intake valve closing timing greatly change in accordance with a change in the intake valve operating angle when the amount of intake air is to be controlled in accordance with the intake valve operating angle.
As a result of phase coupling, the conventional variable valve mechanism described above changes the valve body closing timing greatly when the operating angle changes, as described earlier. In a non-throttle type internal combustion engine, therefore, this variable valve mechanism can control the amount of intake air with sufficiently high accuracy.
The applicant of the present invention has acknowledged that the following documents relate to the present invention in addition to the above-mentioned document.
[Patent Document 1] Japanese Patent Laid-open No. 2002-371816
[Patent Document 2] Japanese Patent Laid-open No. 2001-123810
[Patent Document 3] Japanese Patent Laid-open No. Hei 10-169421